Irish pride, 4GB isn't as bad as your probably think it is. That's more than enough for even the most intensive of tasks, and gaming. Remember that only 64-bit OSes can use more tan 3.25GB of RAM.
If you decide to use 4 sticks of ram instead of 2, on most motherboards you have to manually set the ram voltage. Just add 2 sticks first, turn on, open the bios and set your ram to the manufactures recommended settings, save, turn off . Now add your second set. In some cases you may need to up the voltage one or two steps.
One thing like "Lavarin" said, if you're running a 32bit OS, just go with 2 sticks (4gigs) and save yourself the headache.